You can use side reins with a saddle or roller, just slip the side reins though the girth if using a saddle.
I only use side reins once the horse is accepting of a contact under saddle, and lunges well off voice commands, and will go forward easily when asked. If you have problems with forwardness on the lunge, you're going to accentuate those problems with side reins as the horse will hit the contact and want to stop, and sometimes they will go to the extreme of flipping themselves over when they feel that pressure - so you REALLY need to know what you're doing with them.
Keep them loose for the first few attempts in them, but not loose so they're dangling and going to create uneven pressure on the bit. There should be a contact, when the horse reaches forward a little in a comfortable, working frame, but not pulling the horse's head into it's chest.
The biggest factor is forward when using side reins. If you don't have forward, they have no purpose and will probably be detrimental, teaching the horse to suck back off the contact or brace onto it.